Spring support



L. S. SUOZZO SPRING SUPPORT Jan. 21, 1964 Filed Aug. 9, 1960 4 Sheets-Sheet l INVENTOR. LEONARD S. SUOZZO ;TTORNEY L. S. SUOZZO SPRING SUPPORT Jan. 21, 1964 4 Sheets-Sheet 2 Filed Aug. 9, 1960 FIG.4

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INVENTOR.

LEQNARD S. SUOZZO ATTORNEY L. S. SUOZZO Jan. 121, 1964 SPRING SUPPORT 4 Sheets-Sheet 4 Filed Aug. L9, 1960 FIG. l0

HORIZONTAL (FoRcE)@ Pt.l=X- n3 Ptl Pt2= x .813

INVENTOR. LEONARD S. SUOZZO BY Q 2 ATTORNEY nited States atet 3,118,643 SPRENG SUPPORT Leonard S. Suozze, Hachensach, N.J., (50 Church St, New York 7. N.Y.) Filed Aug. 9, 196%, Ser. No. 48,535 17 (Iiaims. ((11. 248-54) This invention relates to the art of support devices and, more particularly, to spring-controlled support devices for properly and adequately supporting a load and for permitting movement of the load as may be required by conditions of use.

Elle primary object of this invention is to provide a spring-actuated support device having improved structural features and operational characteristics.

Another object of the invention is to provide a support device that is adapted to properly support a load and simultaneously permit substantial travel of the load, as required by conditions of use at a particular time.

The invention has for another Object the provision of a spring support having two principal units, namely (1) a pantograph unit comprising a plurality of links which are pivotally interconnected to form at least one extensible or contractible frame, one end of the pantograph unit being adapted to be secured to a supporting structure and the other end being connected to a load-carrying unit, and (2) a spring device including a housing, a pair of levers pivotally connected to the housing and to corresponding links of the pantograph unit, a pair of rod members pivotally connected to corresponding levers, and spring means cooperatively associated with the rod members to simultaneously actuate the rod members and the levers and effect corresponding extension or contraction of the pantograph unit.

A further object of the invention is to provide a spring support of the character indicated that may have the attributes and characteristics of and serve as a constant support device or a variable support device depending on the specific design employed and the relationship of the spring means to other parts.

An additional object of the invention is to provide a spring support that is sturdy and durable in construction; that is reasonable in manufacturing, installation and maintenance costs; and that is capable of performing its intended functions in a dependable and trouble-free manner.

The spring support of this invention has a wide variety of functions and uses. It may be utilized in many loca tions to support various types of loads. It is useful, for example, in both conventional and nuclear power plants for adequately supporting piping arrangements while permitting substantial movement of the piping as a result of expansion or contraction thereof, due to temperature changes in the material of the piping.

The device is also useful for supporting and maintaining Wires, cables and the like under proper tension. It is especially useful in electrified railroads which employ electrically conductive trolley wires. Such wires are usually strung between spaced vertical columns or poles and the spans between pairs of successive columns are frequently quite long. As a consequence, the length of wire in an individual span may expand and contract substantially due to variations in ambient temperature and use conditions. This results in corresponding variations in both the sag and the tension of the wire in a span. The sag of the wire may vary from a few inches to 24 inches, or more, and the tension may vary correspondingly. A number of items of equipment, such as pulleys, chains and counterweights have been employed heretofore to provide requisite support for the wires. These items have not been entirely satisfactory, however.

My spring support is adapted to be used (1) as a suspension type support device for suspending and adequately supporting a load from an overhead supporting structure, such as a beam, or (2) as a base or floor type support device for adequately supporting a load that is positioned thereabove and that exerts a downward thrust thereon. When used as a suspension type support device, the apparatus of this invention may function as a constant support device by employing a variable force spring unit. Alternatively, the apparatus may function as a variable support device by employing a constant force spring unit. When used as a base or floor type support device, the apparatus of this invention may function as a constant support device by employing an increasing force spring unit and, alternatively, may function as a variable support device by employing a constant force spring unit. In any case, the spring means forming part of my support device may comprise one or more helical springs or disc springs, depending on the design of the device and the relationship of the spring means to other parts.

The incorporation of a pantograph unit in my support device constitutes one of the important features of the invention. It will be apparent to persons skilled in the art from the ensuing detailed description and the accompanying drawings that, while the supporting force of the device may remain substantially constant, any change in overall length of the device and, therefore, in the travel of the load, is in direct proportion to the number of linkage frames or sections which are present in the pantograph unit. Thus, for each increment of extension or contraction of one frame of the pantograph unit, the load travels a distance equal to such increment times the number of frames in the pantograph unit, where the frames are of equal size and like configuration.

The spring unit constitutes another feature of the invention. This unit includes a housing, a pair of levers pivotally connected to the housing and adapted to be pivotally connected to corresponding links of the pantograph unit. The spring unit also includes a single spring means cooperatively associated with the levers for simultaneously actuating both levers to correspondingly extend or contract the pantograph unit. While the spring unit is especially useful with a pantograph unit, it may be employed independently of a pantograph unit to support various types of loads. When employed without a pantograph unit, one lever to the spring unit is secured to a supporting structure and the other lever is connected to the load-carrying unit.

The enumerated objects and other objects, together with the advantages of the invention, will be readily understood to persons trained in the art from the following detailed description and the accompanying drawings which respectively describe and illustrate a complete spring support of this invention and several modifications thereof.

In the drawings wherein like reference characters denote corresponding parts throughout the several views:

FIG. 1 is a view in front elevation of a spring support constructed in accordance with this invention;

P16. 2 is a side elevation view of the spring support shown in FIG. 1, as viewed from the right of FIG. 1;

FIG. 3 is a view in enlargement taken along staggered line 3-3 of P16. 1, parts being broken away for better illustration;

FIG. 4 is a front elevation view of a modified form of spring device, corresponding to the device shown in FIG. 3;

FIG. 5 is a central vertical cross sectional view, in enlargement, of the device shown in FIG. 4;

FIG. 6 corresponds to FIG. 4 and illustrates another modification of the invention;

FIG. 7 corresponds to Fla. 6 and illustrates a related modification of the invention;

PEG. 8 is a view corresponding to FiG. and illustrates a further modification of the invention;

FlG. 9 is a force diagram derived from a spring support of this invention and employing a constant force spring device; and

FIG. ll) is a force diagram derived from a spring support of this invention and employing a variable force spring device.

Referring initially to l and 2 of the drawings, 1 have illustrated therein an overhead supporting structure, such as a beam 15, that carries a T-shaped bracket 16. A pantograph unit P is suspended from bracket 16 by a pivot pin 17. The pantograph unit includes a plurality of links, namely links L-l, 1-2, 1-3, L-d, L-5 and 11-6. Links 1-1 and L-Z are pivotally connected to each other and to bracket 16 by pin 17. Link 1-1 is pivotally conected to link 1-3 by a pin it; having a central part 19 of enlarged diameter which maintains these links in space. -apart relation as shown in 2. Link L-Z; is pivotally connected to link L-d by a pin 2-9; link L-di pivotally connected to link 1-3 by a pin 21 and to link L-5 by a pin 2122; link L-3 is pivotally connected to link L-S by a pin 23; and link 1-5 is pivotally connected to link L-d by a pin 24. As in the case of pin 18, pins 2 through 24 are provided with central parts of enlarged diameter which are positioned between and maintain corresponding links in spaced-apart relation.

Links L-l and L-Z, the portion of link L-3 between pins 18 and 21 and the portion of link L-d between pins 2%) and 21 form an upper frame. Similarly, the portion of link L-3 between pins 21 and 23, the portion of link L-4 between pins 21 and 22 and links 1-5 and 1-5 form a lo 'er frame. Thus, the pantograph unit, as illustrated, forms two frames h ving certain common parts. The pantograph unit is disposed verti ally and is extensible and contractible in a vertical direction. Extension or contraction of one of the frames causes corresponding extension or contraction of the other frame. The referredto frames are in the nature of equilateral parallelograms.

1y increment or" vertical extension or contraction of one of the frames results in twice such extension or contraction for the entire illustrated pantograph unit. In other words, the total extension or contraction of the pantograph unit equals the extension or contraction of one of the frames times the number of frames. it will be appreciated that the pantograph unit may include any desired number of frames, depending on conditions of use, the size and configuration or" individual frames and the desired total travel.

The spring support includes a load-carrying unit 25 which, for purposes of illustration, is shown as comprises a rod 26 having an eye 27 that forms a pivotal connection with pin 24-. A load is adapted to be connected to the load-carrying unit in any manner known to the art in depending relation to the load-curying unit and the pantograph unit.

Mounted on and cooperating with the pantograph unit, in a manner to be described further along herein, is a spring device 58 which includes a support or housing consisting of a tubular side wall 31 and a pair of spaced end walls 32 and 33. End wall 32 has a central through opening 34 and is welded to the side wall, as indicated at 35. End wall 33 has a central through opening 36 and is welded to the side wall, as indicated at 37. Openings 34 and 36 are aligned and coaxial with the housing side wall. A first pair of spaced brackets 38 are secured to housing end wall 32, preferably by welding, and projects laterally therebeyond. Gne end or" a first lever 49 is positioned between brackets 33 and is pivotally connected thereto by a pin ll. The other end of lever 49 is pivotally connected by a pin 42 to a bracket 43 which is afiixed to link L-l. A first rod member 44 consists of a central portion or shank 45, a yoke as and a hollow guide eled. ment 47. Shank 4-5 is slidable in opening 34 of end wall 32. Yoke d6 is pivotally connected to lever 49 by a pin 4*.

A pair of second brackets 49, which are preferably identical with brackets 35, is aiilxed to and projects laterally beyond housing end wall 33. One end of a second lever 5% is positioned between brackets 49 and is pivotaliy connected thereto by a pin 51. The other end of lever 59 is pivotally connected by a pin 52 to a bracket 53 which is affixed to link L-Z. A second rod member 54 consists or a shank 55, a yoke 56 and a hollow guide element 57. Shank 55 is slidable in opening 36 of end wall 33. Yoke 55 is pivotally connected to lever Si? by a pin 53. Levers 4d and 50 are preferably identical and coplanar. Rod members 45 and 55 are also preferably identical and are coa: The axes of pivot pins 41, d2, 48, 51, 52 and 53 are all substantially parallel.

Positioned within the housing is a rectilinear guide tube 6%. Ti e ends of this tube register with and are slidable in the openings defined by rod guide elements 47 and 57. Guide tube 6t carries a series of pairs of oppositely disposed disc springs 61 which may be the same or similar in construction and arrangement to those shown in my Patent N0. 2,, 39,663, granted lune 7, 1960 for Constant Support Device. A spacing ring 62 is provided between successive pairs of disc sprin s 61 and between each end disc spring and the corresponding inner ends of rod memers 4d and Disc springs 61 and other parts within the housing are so constructed and arranged as to normally urge rod member 4 in one direction, i.e. toward the left as viewed in FIG. 3, and rod member 54 in an opposite direction, i.e. toward the right, to the extent allowed by elements 4'7 and 57 of the rod members and housing end walls 32 and 33. At the time the spring device shown in FIG. 3 is assembled, disc springs 61 are precompressed to any desired extent. These springs may be precompressed so as to operate within the deflection range of constant force, as disclosed in my said Patent 2,939,663, so that the spring device may function as a constant load support. The springs may be precompressed so that the spring device functions as a variable support device, if desired.

The loading on the spring device may be controlled by a means 63 which is independent of the spring device and which also limits extension or contraction of pantograph unit 1. Means 63 includes angle brackets 64 and 65 which are secured to links L-3 and L-d, respectively. These brackets are provided with aligned openings (not shown) to receive, support and permit axial movement of a threaded rod 65. This rod is equipped with four nuts, namely nuts 67, 63, 69 and 7%. Nuts 67 and 68 are disposed to opposite sides of bracket 64 while nuts 69 and 70 are disposed to opposite sides of bracket 65. Nuts 57 and 70 limit vertical contraction of the pantograph unit and, therefore, relative outward movement of rod members 44 and 54. Nuts 68 and 69 limit vertical extension of the pantograph unit and compression of the springs in spring device 30. It will be evident that adjusting means 63 may cooperate with other parts to limit deflection of disc springs 61 within the range of constant force or may permit the disc springs to exert a variable force depending on the adjustment of nuts 67 through 7%? relative to rod 66.

For the purpose of outlining the operation of the form of the invention shown in FIGS. 1, 2 and 3, it is assumed that the apparatus is assembled and that the parts are in the relative position shown in these views. It is also assumed that a load, such as piping, is connected to load-carrying unit 25 in depending relation to pantograph unit P. The parts are normally in the relative position shown in FIGS. 1 and 3. Downward movement of the load will cause the pantograph unit to be extended vertically, as indicated by the dot-dash lines in FIG. 1. This causes levers 4t? and .5 to be pivoted about their several corresponding axes and to effect inwmd movement of both rod members 44 and 54 and compression of the disc springs 61 within the housing. Vertical extension of the pantograph unit and, therefore, corresponding movement of the parts of the spring device 33 are limited by engagement of nuts (i3 and 69 with brackets 64 and 65, respectively.

FIGS. 4- and 5 illustrate a modified form of spring device 75 according to this invention. Device 75 has a number of parts which are preferably the same as corresponding parts of device 3i earlier described, and which are identified by like reference numerals. Among such parts are a housing consisting of a tubular side wall 31 and spaced end walls 32 and 33, a pair of levers 4i) and 5t and pairs of brackets 38 and 49. As in the case of device 30, lever 49 of device 75 is pivotally connected to brackets 33 by a pin 41 and is adapted to be pivotally connected to link L-l of the pantograph unit P. Also, lever 5% is pivotally connected to brackets 45* by a pin 51 and is adapted to be ivotally connected to link L-Z of the pantograph unit.

Positioned within the housing is a pair of spaced, dished, movable plates 76 and 77. Plate 76 has a circular flange 78 and is provided with a central opening and a pair of openings 81 and 82 which are equidistant from opening St). Plate 77 also has a circular flange 83 and is provided with three through openings, namely opening 84 which is aligned with opening 80, opening 85 which is aligned with opening 81, and opening 36 which is aligned with opening 82. A U-shaped connector 87 consists of a web 88, having an opening 89, and a pair of arms 94) and 91. Arm 9%) is freely movable through plate openings 81 and 85 while arm 91 is freely movable through openings 82 and 86. The free ends of arms 98 and 9?. are threaded to receive corresponding nuts 92 and 93, respectively.

A helical compression spring 95 is positioned within the housing and bears at its ends against plate flanges 78 and 83 to normally urge the plates away from each other.

One end portion of a first rod member 96 extends through opening 89 and carries a nut 97. The other end of this rod member is in the form of a yoke 93 which is pivotally connected to lever by a pin 99. A second rod member 1% extends through plate openlugs 84 and S9 and carries a nut 191 at its inner end. This rod member also extends through opening 36 of housing end wall 33. Rod member 1% includes a yoke 102 at its outer end which is pivotally connected to lever 5% by a pin 193. The parts are normally maintained in the relative position shown in FIGS. 4 and 5 due to the action of spring 95. The spring device 75 is adapted to be connected to the pantograph unit in the same manner as device 39 and operates in a manner similar to the earlier described form of the invention, as will be evident from an examination of the drawings.

The constructions shown in FIGS. 1 through 5 contemplate spring devices in which the pivotal connections between each lever 40 and 50 and corresponding associated parts lie in a common plane, i.e. the pivotal axes of pins 41, 48 and 42 of lever 42' (FIG. 3) lie in one common plane while the corresponding pivotal axes of lever 50 (FIG. 3) lie in another common plane. Similarly, the pivotal axes of the pins of each lever of FIG. 4

ie in a common plane.

The constructions shown in FIGS. 6 and 7 correspond to that shown in FIG. 4 except that the pivotal axes of the corresponding levers are not coplanar. Referring to FIG. 6, the modification of the invention depicted therein includes a spring device 1% which is generally the same as that shown in FIG. 5. Device ltlS difiers over that of FIG. 5 in the relationship of levers 166 relative to other parts. Levers 166 are identical but reversed. Each of these levers is provided with openings 167, 168 and It)? to receive pivot pins corresponding to those earlier described and adapted to connect with other parts also earlier described. It will be observed that opening 103 of each lever is positioned outwardly beyond a plane extending through corresponding openings 197 and 199. This varies the force exerted by the spring means of the device from that of FIG. 4 during use.

The modification shown in FIG. 7 illustrates a spring device having a pair of identical but reversed levers 111 that are provided with openings 112, 113, and 114 to receive corresponding pivot pins earlier described.

Reference is next had to FIG. 8 which illustrates a further modification of the invention. The spring device 115, illustrated in this view, includes a number of parts which are the same as corresponding parts of earlier described forms of the invention. Device 115 also includes a U-shaped member 116 corresponding to member $7 of FIG. 5. Positioned between movable plates 77 is a first helical spring which normally urges the plates away from each other. A second helical spring 118 is positioned between housing end wall 32 and one movable plate While a third helical spring 119 is positioned between housing end wall 33 and the other movable plate. Any one of the lever arrangements earlier described may be employed with device 115. The action and the effect of springs 117, its and 1-19 on movable plates 77, U- shaped member 116 and rod members as and ltlil will be evident from an examination of FIG. 8 without further description.

In each of FIGS. 9 and 10:

A represents the axis of pivot pin 17; B represents the axis of pivot pin 26; and C represents the axis of pivot pin 21.

The legends and data appearing on the drawings containing FIGS. 9 and 10 taken in conjunction with the corresponding force diagrams shown in these views bring out that, by employing a constant force spring device with the pantograph unit, the apparatus may be transformed into one having the functions and characteristics of a variable support device and, by employing a variable force spring device with the pantograph unit, the apparatus may be transformed into one having the functions and characteristics of a constant support device. Whether the apparatus will be capable of serving as a variable support device or as a constant support device is a matter of design within the skill of persons versed in the art. The important thing to bear in mind is that the apparatus of this invention is capable of functioning and being used as a variable support device or as a constant support device, depending on the particular design embodied therein.

It should also be borne in mind that either disc springs or helical springs may be employed alone or in combination with each of the several terms or" the invention described herein. Moreover, the various spring devices shown in the drawings may contain one or more disc springs or helical springs or combinations of such springs,

spending on the requirements of a particular design.

The term pantograph is used in this description and the accompanying claims to identify extensible and contractible linkage arrangements of the general type shown in the drawings. The pantograph unit may include any number of frames to effect desired travel. While the frames of the pantograph unit are preferably identical in size and in the form of equilateral parallelograms, it should be borne in mind that individual frames may difier in size and may have configurations other than a parallelogram.

The illustrated complete spring support is shown in H65. 1 and 2 as being suspended from an overhead supporting structure to carry a load which exerts a downward pull. The device may be inverted from the position shown in FIGS. 1 and 2 and used as a fioor type '7 support with the load applied above and acting downwardly on the device.

From th foregoing, it is believed that the construction, operation, objects and advantages of my present invention will be readily comprehended by persons skilled in the art, without further description. It is to be clearly understood, however, that various changes in the const uctions described above and illustrated in the drawings may be made without departing from the scope of the invention, it being intended that all matter contained in the description or shown in the drawings shall be interpreted as illustrative only and not in a limiting sense.

I claim:

1. in a support device of the character described, a linkage unit including a plurality of links, said links being obliquely positioned and pivotally interconnected to form at least one vertically extensible and contractible frame, a spring device comprising a support unit, a pair of levers, one of the levers being pivotaily connected at one end to the support unit and at its other end to at least one of the links, the other lever being pivotally connected at one end to the support unit and at its other end to at least one other link, a pair of rod members, each rod member being pivotally connected to a corresponding lever, spring means carried by the support unit and cooperatively associated with the rod members for normally biasing both rod members simultaneously in a manner to impart corresponding pivotal movement to the levers and to the links of th frame, and means independent of the spring device and connected to at least two of the links for limiting vertical extension and contraction of the frame.

2. A support device according to claim 1 wherein the levers are substantially coplanar and wherein the axes of the pivotal connections between the levers and the support unit are spaced and substantially parallel.

3. A support device according to claim 1 wherein the rod members are substantially coaxial and wherein the spring means normally biases the rod members in opposite directions.

4. A support device according to claim 1 wherein the levers are substantially coplanar, wherein the axes of the pivotal connections between the levers and the links are spaced and substantially parallel, wherein the rod members are substantially coaxial and wherein the spring means normally biases the rod members in opposite directions.

'5. A support device according to claim 1 wherein the lovers are substantially coplanar; wherein the axes of the pivotal connections between the levers and the support unit, between the levers and the links and between the levers and the rod members are spaced and substantially parallel; and wherein the pivotal connection between each lever and its rod member is intermediate the pivotal conaction between that lever and the support unit and between that lever and the corresponding link.

6. A support device according to claim 5 wherein the rod members are substantially coaxial and wherein the spring means normally biases the rod members in opposite directions.

7. A support device according to claim 6 wherein the spring means comprises at least one disc spring.

8. A support device accordin to claim 6 wherein the spring means comprises at least one helical spring.

9. In a support device of the character described, a

pantograph unit comprising a plurality of links, said links r2 device for actuating links of the pantograph unit to normally urge the load-carrying unit in one vertical direction, said spring device comprising a sup ort unit, a pair of levers, one of the levers being pivotally connected at one end to the support unit and at its other end to at least one of the links, the other lever being pivotally connected at one end to the support unit and at its other end to at least one other link, a pair of rod members, each rod member being pivotally connected to a corresponding lever, and spring means carried by the support unit and cooperatively associated with the rod members for normally biasing both rod members simultaneously in a manner to impart corresponding pivotal movement to the levers and to the links of the frame.

10. In a spring device, a housing, a pair of coaxial rod members carried by the housing, spring means within the housin and cooperatively associated with the rod members for normally imparting axial movement to one of the rod members in one direction and to the other rod memher in the opposite direction, and a pair of levers, one of the le ers being connected and movable relative to the housing about a first pivotal axis and to one of the rod members about a second pivotal axis, the other lever being connected and movable relative to the housing about a third pivotal and to the other rod member about a fourth pivotal axis, said axes being spaced from each other and substantially parallel.

ii. A spring device according to claim 10 wherein the spring means comprises at least one disc spring.

12. A spring device according to claim 10 wherein the spring means comprises at least one helical spring.

13. in a spring device, a support unit, first and second levers, the first lever being connected and movable relative to the support unit about a first pivotal axis, the second lever being connected and movable relative to the support unit about a second pivotal axis, first and second rod members, the first rod member being connected and movable relative to the first lever about a third pivotal axis, the second rod member being connected and movable relative to the second lever about a fourth pivotal axis, and spring means carried by the support and cooperatively associated with the rod members for normally biasing both rod members simultaneously in a manner to impart corresponding pivotal movement to the levers about their axes, the first lever being adapted to be connected and movable relative to a supporting structure about a fifth pivotal axis, the second lever being adapted to be connected and movable relative to a load-carrying unit about a sixth pivotal axis, the third pivotal axis being intermediate the first and fifth pivotal axes, the fourth pivotal axis being intermediate the second and sixth pivotal axes.

14. A spring device according to claim 13 wherein said pivotal axes are spaced from each other and substantially parallel, wherein the levers are substantially coplanar, wherein the rod members are substantially coaxial and wherein the spring means normally biases the rod members in opposite directions. 1 a

15. A spring device according to claim 14 wherein the first, third and fifth pivotal axes lie in a common plane and wherein the second, fourth and sixth pivotal axes lie in another common plane.

16. A support device according to claim 14 wherein the first and fifth pivotal axes lie in a common plane which is intermediate the third pivotal axis and the spring means and wherein the second and sixth pivotal axes lie in another common plane which is intermediate the fourth pivotal axis and the spring means.

17. A spring device according to claim 14 wherein the third pivotal axis is intermediate the spring means and a plane which is common to the first and fifth pivotal axes and wherein the fourth pivotal axis is intermediate the spring means and another plane which is common to the second and sixth pivotal axes.

(References on following page) 9 References Cited in the file of this patent 2,535,305 a 2,908,491 UNITED STATEQ PATENTS 2,939,663 1,612,163 Todd Dec. 28, 1926 1,893,295 Bailly Jan. 3, 1933 5 2,395,730 Farkas Feb. 26, 1946 409,973

10 Loepsinger Dec. 26, 1950 Suozzo Oct. 13, 1959 Suozzo June 7, 1960 FOREIGN PATENTS Germany Feb. 18, 1925 

1. IN A SUPPORT DEVICE OF THE CHARACTER DESCRIBED, A LINKAGE UNIT INCLUDING A PLURALITY OF LINKS, SAID LINKS BEING OBLIQUELY POSITIONED AND PIVOTALLY INTERCONNECTED TO FORM AT LEAST ONE VERTICALLY EXTENSIBLE AND CONTRACTIBLE FRAME, A SPRING DEVICE COMPRISING A SUPPORT UNIT, A PAIR OF LEVERS, ONE OF THE LEVERS BEING PIVOTALLY CONNECTED AT ONE END TO THE SUPPORT UNIT AND AT ITS OTHER END TO AT LEAST ONE OF THE LINKS, THE OTHER LEVER BEING PIVOTALLY CONNECTED AT ONE END TO THE SUPPORT UNIT AND AT ITS OTHER END TO AT LEAST ONE OTHER LINK, A PAIR OF ROD MEMBERS, EACH ROD MEMBER BEING PIVOTALLY CONNECTED TO A CORRESPONDING LEVER, SPRING MEANS CARRIED BY THE SUPPORT UNIT AND COOPERATIVELY ASSOCIATED WITH THE ROD MEMBERS FOR NORMALLY BIASING BOTH ROD MEMBERS SIMULTANEOUSLY IN A MANNER TO IMPART CORRESPONDING PIVOTAL MOVEMENT TO THE LEVERS AND TO THE LINKS OF THE FRAME, AND MEANS INDEPENDENT OF THE SPRING DE- 